Application of the ramp test from a closed cavity rheometer to obtain the steady-state shear viscosity η((γ) over dot)

The steady-state shear viscosity beta((gamma) over dot) is required in controlling processing parameters for the extrusion processing of polymer melts. A new method, the so-called ramp test, is investigated in this study to obtain the steady-state shear viscosity with a closed cavity rheometer (CCR). To verify the method and the accuracy of the CCR data, three commercial polyolefin polymers, a low-density polyethylene (LDPE), a linear low-density polyethylene (LLDPE), and a polybutadiene (PBD), were used as model systems. Measurements of the magnitude of the complex viscosity vertical bar eta(omega)vertical bar were compared with the steady-state shear viscosity data obtained by capillary rheometer and CCR. Further, time-temperature super-position master curves of the magnitude of the complex viscosity and steady-state shear viscosity obtained by CCR were developed for LLDPE and PBD. The influence of the cavity sealing on the instrument's accuracy to obtain the steady-state shear viscosity was investigated using the finite element method simulations. Thus, it was shown that the ramp test performed by CCR is a practical method to determine reliable and reproducible data of the steady-state shear viscosity within a wide range of temperatures (T = 50-180 degrees C) for low and high viscous materials (vertical bar eta*(omega)vertical bar = 1.6-480 kPa s, M-w = 144-375 kg mol(-1)).

Automated summary

This study investigated a new method called the ramp test to obtain the steady-state shear viscosity of polymer melts using a closed cavity rheometer (CCR). The method was verified using three commercial polyolefin polymers and it was shown that the ramp test performed by CCR is a practical method to determine reliable and reproducible data of the steady-state shear viscosity within a wide range of temperatures for low and high viscous materials.